Erioderma pedicellatum : an ecophysiological study of a globally threatened pioneer lichen on thin spruce branches in old forests
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- Master’s theses (MINA) 
Lichen extinction occurs at a fast rate due to human activity, and species yet to be discovered are likely go extinct every year. Many species close to extinction may still be rescued by conservation management based on an understanding of species-specific habitat requirements and physiological responses. Erioderma pedicellatum is close to extinction and only known at a few sites world-wide. To prevent this species from going extinct, we need to know its ecophysiological responses and why it is rare. At its last remaining site in Europe, Tegningfallet in Norway, a spatially restricted population of 1500-2000 thalli dominate the epiphytic vegetation in a few Picea abies trees in a canyon with a waterfall. Microclimatic conditions at the site show that E. pedicellatum demands high-light conditions in combination with high relative humidity and relatively cool temperatures. It further requires unusually high pH branches of Picea abies. Erioderma pedicellatum has a high CO2 and O2-uptake under suitable conditions, experiences suprasaturation depression of photosynthesis at high water contents, and its growth rate was reduced with increasing thallus size. Too humid conditions appeared harmful for the species. Erioderma pedicellatum tolerates desiccation in combination with light well, but the population at Tegningfallet is shaded from direct sun light during the entire winter. Optimum temperature range for photosynthesis occurred at 10-15 °C, temperatures ≥25 °C significantly reduced carbon gain. Morphology and functional hydration traits significantly differed between the Tegningfallet and Newfoundland populations, in line with the different hydration sources in these two habitats. Understanding why and how E. pedicellatum can exist at a site such as Tegningfallet is essential for understanding how we can prevent this species from going extinct, and the presented results should encourage new management action plans and further research at the other remaining sites of the species. Methods used in this thesis could also be applicable for ecological understanding of other lichen species at risk of extinction.